Control mechanism for engine driven compressors



May 19, 1953 H. H. RAMBo 2,539,083

' CONTROL MECHANISM FOR ENGINE DRIvEN coMPREssoRs May 19, 1953 v H. H. RAMBo Y 2,639,083

CONTRCL MECHANISM FOR ENGINE DRIVEN COMPRESSQBS I Filed May s, 194e v s sheets-sheet 2 /G i l I INVENTOR.

HOWARD H. RAMBO Arron EYs May 19, 1953 H. H. lfla/Mao 2,639,083

` CONTROL MECHANISM FOR ENGINE DRIVEN 'COMPREssoRs Filed May 8, 1948 3 Sheets-Sheet 5 o m 0 m :E u.) n: o. Z o u IUI q' er 'D f 5 154 Q' E I m gp Z DI z m IN V EN TOR H owA R0 H. RA M50 ATTORN YS Patented May 19, 1953 i COISTIROLJ MECHANIS'M'-1FOR ENGINE DRIVEN COMPRE SSORS Howard -H.Ra-mbo, West Ghetelf, Pa., .assignorto .Schramm, Inc., West tion `oit' Rennsylvania .Chcsteixj Pa., .a .corpora- Application MayfS, 1948;: SerialgNon215888 ...Thisinvention-relates:Lto-.control'means for-:engine .driven V.compressors and .has particularref- .erencey tozthe control and ,'unloading.,of-;a .driving .engine accordance A-with pressures ing-acom- .ppressedeair tank.

1 .-Heretoore .it has ,been customary to .produce .unloading of a Vcompressor when :the pressure-in the air. snpplytank reaches a;.certain maximum value .with ,simultaneous-.freduction c of .the engine speed to .an .idling y:speed afrom .the kfullspeed thereof. .This .condition `:Was then maintained 4,until ,-a :predetermined minimum pressure existed in .ft-he supply `.tankwhereupon theengne .was ...speeded `up. to. full .speed and reloading `of the :compressor occurred. with .some .slight delaynecessaryto permit theengine vto pickupspeed and prcventzfstalling One :of theginost satisfactory .types onunloaiding 1which was .used involvedmain- .taining .openthe inlet valves yof the-compressor ,so that air -drawninto the 4cylinders would vbe .discharged :through the vinlet pqrtsgwithgut 1@Q ,o uirng absorption.of,-large .amounts Qfenergy.

.In the. application of Repscha .and Serial No. .761;092, .zled `July .115, .1947, PatentLNo.

2,-595;369, `May ,6, 1952, @an .improvement ,.iSepIO- posed .involving fcontrolof;` theyspeeduofaan. engine in .proper relationship .to .the ...demands v,on ',.the compressor 1` driven :thereby aand, .infparticulan with. the/.maintenance of operationfamore-011- tinuousnaturethan has occurredheretofore. In accordance .with .the .invention of :that '.appl-ication' .the engine will .operate fat; full speeds/when vthe pressure in thesupplytank is at .its .minimum .value IAs vthis .pressure increases .thefspeed @of `the.v engine will f be .gradually `reduced.' until af-When themaximumpressnre desired inzthesupplytank :is .approached the ...engine :may .be loperating zat half speed orsome. other. suitable.. fractionzofits full speed. .Thenfwhen themaximumxrpressllreg-is reached through; aslight increaseon pressure unloading will occur andthe. enginetwillmbe slowed down'. to an idling speed. As.. air .aisridrawnf from theztank and the. pressure zthereinidecreasesethe eng-ine continues to operate .ata idling `speed :until a predetermined Value i of pressure; is :reached l .when in quick vvsuccession:.thetenginetisazlnoilglit up f. to the speed corresponding .sto zthe pressure inthe tank and. the compressor .is- :reloaded :with .a `repetition vof.` the cycle. iIt:will.abegobviouszthat the. r. cycle just .described `involves `vlongerperiods of xoperation sof .the `.engine 'at speedslessffthan full@ speed when the :demands on ithe: compressor arermdderate, i. :e.,^:. there is anaoperation '.ofsthe engine corresponding morenearly to the'demands on the4 compressor :to .approach:econtinuouspperation. The result .-.is y.less wear-.on the engine as well as onthe'partsfwhichareinvolvedimthe unloading operation.

, The generaholoject of vthe, present inventionds ,to improve Astill further the .characteristicsiof.op- -.era.tion.of an` engine-compressor unit. linac- ;cordance with v.the .present invention the System 4ci the, -Repscha and Foxk application ispreierably .involved .to the. extent that the :engine .speed controlled. However, linstead of. continuing llthe .drive ofthe compressor. when lthe .engine Vis idling, -with. yunloading. in the usual lfashion, the engine is. coupled. to the compressor` .through-.a magnetic vclutch Isogthat. unloading of, the .system is effected :pygcausing disconnection-.of `the clutch-withfthe result thatwhentheengine isidling the compresser. iastationary. yThat thiswsystem .is Satis- -iactoryiin operation is due, to the characteristics ,oia magneticclutch .in.coupling;the engine to the- .compressori in a `transiently yieldinf.; fashion 4so @that although .slippage .is ,..eliminated `almost immediately .after thev clutch is energized, nevertheless the. application yof the .compressor load vto :the :engine issuiciently delayed :that .ther engine .may piel:` up.` thecoinpressor Withoutfstallng; the icnginathrottle being, :of course, .opened-.to vin- ,crcasedts :power simultaneously with @theeen- 'xg-agement yof .the clutch.

Whileas indicated the.invention .desirably,,in .-volyes control Vor the A.engine lspeed dependent .13130.11 the pressure .in the Aair tank, =it is vnot essentiaLgin accordance witlrthe present invention, ,tokprovidefforsuch .continuous 4controlf` of; engine speed, flout rather the --engine :may be operated y,ationly Ltwo speeds, idling speed yandnfjull lInac,cordallce-.withctloe,inventioniitis lsopos- ,sible to ...have anr engine drive rtwo `or more'. corn.- ;pressors soarranged as to involve .a :fairly iconrtinnousoperationf. otone compressor witnaedef -gree .of intermittent operation of fthe `otherfde- Figure 3 is a diagrammatic view illustrating the fashion in which an engine may drive a pair of compressors to achieve the advantages of the present invention.

Referring first to Figure 1, there is indicated at 2 an internal combustion engine which may be of the gasoline driven type or of a diesel type. This is arranged to be coupled through a magnetic clutch indicated generally at 4 and shown in detail in Figure 2 to a compressor 6. The advantages of the invention are particularly great when the compressor is of the positive displacement piston type but, as will be evident to those skilled in the art, the invention is applicable to the drive of other compressors, for example centrifugal compressors.

Various parts illustrated in Figure 1 will be found to have their counterparts in said Repscha and Fox application and in Gustafson Patents 2,023,418 and 2,160,860 dated, respectively, December lo, 1935, and June 6, 1939. The compressor is illustrated as delivering compressed air through a connection 8 to the air supply tank I0 from which it is withdrawn as used. A line I4 receives air from the tank through a water and oil lter I2 of conventional type and is arranged to deliver air through the connection I6 to an unloader valve I8. This comprises a casing 20 in which is located a disc 22 operating between a lower seat 26 and an upper seat 28, the disc being normally urged downwardly by a spring 24. The space above the seat 28 is open to the atmosphere. The space below and inside the seat 26 is connected to the line I6. Reference to the aforementioned Gustafson patents will reveal that the unloader valve is essentially as indicated in those patents. An air delivery connection 30 serves to feed air when the disc 22 is in upper position to an air switch device comprising a housing 32 provided with a cylinder bore 34 in which is located a piston 36 arranged to act upon a spring 38 secured to the body 42 of a conventional microswitch, the arrangement being such as to operate the button 40 of that switch. Downward movement of the piston 36 is limited by a transverse pin 31. A connection 44 from this air operated switch device leads to a control device which also receives air directly from the line I4 through the connection 43.

The control device which is indicated generally at 46 involves members forming a housing in which are mounted diaphragms 48 and 54 to define a lower chamber 50 in communication with the line 43 and an intermediate chamber 52 in communication with the line 44. A spacer 56 is located between the diaphragms and the upper face of the diaphragm 54 carries a member 58 on which bears a roller 60 carried by a lever 62 pivoted to the device 46 at 64. The lever 62 is urged downwardly by a tension spring 65 and also by an adjustable compression spring 66, the pressure exerted by which is varied through nuts 68. A link connects the end of lever 62 with the throttle valve 12 in the intake connection 14 of the engine 2. The intake connection 14 is connected to the carburetor and intake manifold of the engine. It may be here noted that in the diagram of Figure 1 in orderto promote clarity the parts are not indicated in their conventional physical relationships; for example, usually the air tank is mounted directly adjacent to the cornpressor and, of course, the intake connection of the engine would normally be mounted directly thereon. It may also be noted that while direct control of a throttle is illustrated as would be the normal control in the case of a gasoline engine, the control might well control a conventional governor which in turn controls the throttle, and in the case of a diesel engine the connection 10 might control the operation of a fuel valve or pump or the conventional governor. In any event, the power output of the engine is controlled through movement of the lever 62.

The diaphragms 48 and 54 are flexible and hence the effective area of the diaphragm 48 is the area of the spacer 56 in contact with it, while the effective area of the diaphragm 54 is the area of the member 58 in contact with it. The latter area will be noted to be substantially greater than the former. It is also to be noted that the roller 60 as arranged on the lever 62 is such that as movement is imparted to the lever the effective lever arm at the roller 60 is substantially increased. This is desirable for the most satisfactory type of operation.

The electrical elements of the system illustrated in Figure 1 are illustrated as energized from a battery 16 which will, of course, have conventional connections to a charging generator and to an engine starting motor. Since these and other details, including safety devices, are conventional they are not illustrated and the electrical connections in the diagram are reduced to their elemental form. A main switch I8 is indicated, manual closure of which supplies current to the microswitch 42 and to a relay 80 which is controlled by the microswitch. The relay which is of conventional type is preferably a mercury relay and is interposed in the system merely because it will tolerate inductive surges of current which are produced in the magnetic clutch circuit. This relay 80 controls the ow of current to the clutch 4 through the lines 82 in which are interposed a manual switch 84 in parallel with a temperature-responsive switch 86 operated through a conventional connection to a thermally responsive liquid-containing bulb 88 which is located adjacent to the engine to respond to a warmed-up condition of the engine; for example, by being immersed in the cooling water system of the engine. The object of this switch is to permit closing of the magnetic clutch circuit, when the manual switch 84 is open only after the engine has warmed up to a suitable operating temperature. By the use of this arrangement the engine may be started but even though pressure conditions are such that the clutch 4 would normally be engaged, until the engine has warmed up, the clutch will not be energized and hence the compressor will remain idle. This is particularly desirable for the initiation of operation in very cold climates where injury to the engine might result if it were loaded when cold. For purposes of general description, however, it will be assumed that the engine has been warmed upand the switch 86 is closed.

Before proceeding with a description of the operation reference may ,be made to Figure 2 which illustrates a preferred type of clutch used in this system. Brushes 90 and 82 connected `to the lines 82 engage slip rings 84 and 96 to which are connected the terminals of the clutch coil 98 which is carried by the element |00 of the clutch which is keyed to the compressor shaft. Friction material |02 is arranged to be engaged by the plate |04 which is connected te the element of the clutch connected to the engine shaft through pins |06, light springs |08 normally maintaining a light frictional engagement between the plate |04 and the material |02. A

:be :best understood :by :considering-initiallythat ,j

:thetank l0. is at minimumgp-ressure.. Underithese `.conditions the disc f22 -rests fion the seat 26 rand :thelline 30 is Ventedpto the atmosphere .The zzbore 34. of theswitch Yoperator 32 also-.under atmospheric .pressure and .the `rnficreswitcli :112 .will'befclosed. Under; these conditionszthe lrelay 8 0 :closes the; circuit'. throughlthe I.n'lagnetic:clutch and the engine is r`accoridingly. vcoupled :'to .the compressor. -At :this same :.time, through connection 143, .the;.chamber "150 `is subjected' to the tankpressure while I cham'beri 2..-isa underfiatmos- .pheric pressure dueto they connection .of .line 44 with the line 3i) through the switch operatorr32. :The pressure. .in :the chamber aactsfzonly iontthe veiectiye area of contaotzbetweenthediaphragm .48 4and the spacerx. sothatthe upWar-diorce .on'the roller .60.is. acminimum. The :engine is i'accordingly operating .at-full.speed .driving the :compresso-r .which suppliesuair tothe tank.

:As tthe .pressure in the ,tank rises .'the .force 4actingon the roller Bt increases andlthethrottle Valve .1,2 is.nioveidzcorrespondingly toward iclcsed position. .Thefact that .the Valve 46 becomes more and :more eiectivefin throttlingthe. intake as the ylever :62 lchangesitsangleis .taken .care

.of Iby.thef'increasedleyer. arm of the rollerfi, .the `,eiiect lbeing-an increased rate .Ofchange of the `position Aof the lever B2 asthepressure in the `chamber eincreases. vAdjustments 'may be Ymade to secure anydesired reductionin `speed .as the rpressure in .the tank :l .increases For example, .to consider .for .clarityv typical yfigures, letit be assumed:thattheminimumtank pressureis 85 pounds .per squaretinch and under such ,conditions vthat theengine operatesat 1200 R, P..M. Theniat axpressure `suchas:.105 pounds per square inch 4the .controlof the throttle "12 may resultV in ^a decrease ofrthe enginespeedto `600 R. P. M.,.the speedyariation between/.these gures `being continuous with variation.of1pres sure. .If V105'pounds'.perzsquare inch is regarded as the maximum tank :pressure desired then the adjustment `of the pilot lvalveli isfsuch that at about this g. pressure Value the zdisc22 will be snapped upwardly against the seat 28 by the vpressure beneath it with thel result that the tank pressure is kappliedthrough'theline tofthe pneu-matic switch "32 and thence through "the line 44 Itothe cham-berl 52. The snap actionof the pilot valve is'as described in'said Gustafson patents and need not be-repeated here. It need only be noted that thearea of the disc :subjected to the .tank pressure is'substantially increased when it rises from the seat 26 `soI that it'will rnot return to thatseat until Ithe tank `pressure drops quitesubstantially. A' stablesnap :action` is thus secured.

W hen the tank pressure isr applied to the chamberf52 it will then be acting upon the increased area represented by the excess area of the member 58 over the area of the spacer 56 and consequently a considerably greater force acts upon the roller 60. The throttle I2 is accordingly closed to idling position limited by the usual adjustable stop which is not shown. rihe engine accordingly has its speed reduced to idling speed which may, for example, be about 400 R. P. M.

At the same time the action of the air pressure applied to the Apneumatic switch device 32 will cause the microswitch 42 to open its circuit and thereby throughrsthe mercuryirelaycdvopenrthe :gcircuit :to :the magnetic clutch f 4 :disconnecting the :engine .':from :the fcofmpressor. zThe f: engine accordingly mom-es torestandrthistype vdiepere- :tion saves. much fwear on: the compressorfas4 conrtrasted with i. the imode cof `Munloading heretofore used .involving continuous loperation .of the compressor :but fwith .fthe @inlet -.valve held `:open .rito effect unloading. The engine'is, rroi coursaxre- :lieved :of .even :the burden of iturnirrg over :the compressor .i so `that "izsubstantial vLtuelsaving 4'elfected :The conditions just indicated will thenA .continue untilithe' pressure inthe :supply: tank drops to. such value :that the Vspring i524 will force :the zdisc 22 .flownwardly :againstthe-.seatle 'iCenasistent` :with :the '.'gures :previously givenzthis .mightgforexampla.occur at 9.0.po-unds1perfsquare inch. Until this occurs, reven'thoughthetank pressure has decreased, the .engine `throttle @will `not be `opened because :ithe `.increased effective ,diap-hragmrarea yexposed-to:tank pressure is sufrficientrto; yholdrthe throttle .in idling position.y

.ns-xsoon'asthediscJZ is seated at 26 the'lines Ainland L'filtrare yopen Ito the atmosphere. vThe :throttle Will bel opened to provide an engine :speed corresponding to .the1pressure thenexisting :in the'suppiy tank. .At the same timethemicroswitch-42 isclosed and .thefxrnercury.switchliill wilt close'. to energize the kWinding of :the clutched. v The engine and 4compressor y.Willathus `loe :coupled together. While the.. `engagementloffthe clutch and attainment of a condition of nofsliprbetween the enginezand compressor shafts .occupies only a very small interval, nevertheless, it 4liasrbeen found thatthereuis suflicient lagand:slippage to ermit theengineatoassumethe compressori load without ,anydetrimental shock or.l stalling. -The response 4of .theengine-.tothe' throttle is,:of course, veryqrapid inits idleconditionandits riseto fullspeed takesfplace'in only "a rshort interval. .The zself inductance of .the .clutch winding -is suiiicient to cause a slight delay in clutching-and .untiletheicurrent reaches the .-full vValue'in the winding some slippage. may occur. Accordingly, proper y"operation will result. 'It :may /belhcre noted k@that Ia magnetic vclutch rof f the type :illustratedzis designedk in such -fashion asrnot to 4be damaged. bysa"moderate amount "of slippage fbetweenztheiclutch elements and itvhas been found thatrthezliferof a a'clutch inthel present ysystem is Lvverylong and satisfactory.

The-cyclewhich'ha-.s been described will repeat periodicallydepend-ing uponthe demand of'f-air fromthe tank. It will-:be evident that dueto the Acontinuous yvariation of vengine speed ywith supply. tank pressure, there willl bea considerable range :of :demands on the supplytank less than the` maximum demand corresponding to 'which unloading y.Willnot Voccur since". the displacement of r the compressor .isfreduced `.to-fthe demand, throughreduct-ion of speed,V and the tank-pres surewill'rnotf-then rise' to the unloading: pressure. Onlyzundenconditions'of a` demandlless than that correspondingto theilowest controllable speed of the compressor Will the tank pressure rise to the pressure effecting unloading, i. e., throttling of the engine to idling speed and disengagement of the clutch. For sustained periods, accordingly, there will be continuous operation of the compressor at variable speeds less than full speed Without the occurrence of an unloading operation. While this advantage of avoiding numerous starts and stops is attained in the system described in said Repscha and Fox application,

it will be noted that such operation is particularly advantageous in the present system since there is avoided, to a maximum extent, engagement of the clutch which will produce some wear thereon. Not only are the engine and compressor operated at less than maximum speed through considerable periods to reduce wear thereon but the compressor is entirely stopped whenever unloading is achieved.

While as just indicated it is desirable to utilize the control of speed dependent upon pressure through the use of a control device such as 46, it will be evident that this speed control may be replaced by an on-oif type of throttle control such as that of Gustafson Patent 2,023,418, i. e., the control may cause the throttle to be either fully opened or closed to idling position. The advantages of using the magnetic clutch will nevertheless be secured.

The invention may be applied in some cases to the drive of more than one compressor by a single engine. This is illustrated in Figure 3. The engine I6 is here coupled to the compressors ||8 and |20 through the magnetic clutches |22 and |24, respectively. The compressors jointly deliver air through the line |26 to the air tank |28. From this tank the line |30 connects to two pilot valves |32 and |36, each of which may be identical in construction with that illustrated at I8 in Figure 1. The pilot valve |32 controls the pneumatic microswitch indicated at i 34 similar to that previously described which, in turn, controls the mercury relay |35 in the circuit of the clutch |22. The pilot valve |32 has no control over the engine speed.

The pilot valve |36, on the other hand, is connected yin a system which is the same as that of Figure 1, controlling the microswitch |38 and through it mercury relay |40 and clutch |24 and also controlling the operation of the control device |42 corresponding to the control device 46 connected through a linkage |44 to the engine throttle |46.

In the case of the system of Figure 3 the pilot valves |32 and |36 are set differently through adjustment of their springs corresponding to 24 of Figure 1. The pilot valve |32 is arranged to snap to disengage the clutch |22 upon the attainment of a tank pressure less than that required for similar operation of the pilot valve |36. Accordingly, the compressor |20 is the main compressor of the system and operates alone under conditions of such demands as will result in a tank pressure above that required to trip the pilot valve |32. On the other hand, greater demands will involve operation of the compressor I8. This compressor ||8 will then operate considerably less in the aggregate than the compressor |20. As will be evident, a simple switch arrangement may be used to interchange the control connections for the two magnetic clutches so that if it is desired to equalize the lives of the two compressors they may be interchangeably operated as the main and secondary compressors.

It will, of course, be evident that the system 8 of Figure 3 may be extended to the control of three or more compressors if the wide range of demands on the unit make that desirable.

Furthermore, it will be evident that the two clutches may be in series arrangement with respect to the engine; i. e., the engine may drive clutch |24 and through it the compressor |20, while the clutch |22 may be driven from the driven side of clutch |24 and in turn drive the compressor H8, the clutch |24 being thus interposed between the engine and both of the compressors. Depending upon the desired physical arrangement of the engine and the compressors, gear or belt drives may be variously provided, the same being, of course, true of the modication illustrated in Figure 1 as well.

What I claim and desire to protect by Letters Patent is:

In combination, a combustion engine, at least two compressors, a pair of magnetic clutches through which the engine drives the compressors, a tank connected to the compressors to receive compressed gas therefrom, a pair of pressure responsive pilot mechanisms, a first switch means, one of said pilot mechanisms operating in response to pressure in the tank and controlling said rst switch means `when the pressure in the tank reaches a predetermined value to disengage one of said clutches to stop one or" said compressors, a second switch means, the other of said pilot mechanisms operating in response to pressure in the tank when it reaches a value greater than the first mentioned predetermined value to control said second switch means to disengage the other of said clutches to stop the other of said compressors, and means responsive to variations of pressure in the tank throughout a predetermined range of pressure therein to adjust the engine speed within a predetermined range of speeds in response to substantially any change in tank pressure and responsive to operation of said other of said pilot mechanisms to reduce the engine speed to idling speed when both of said compressors have been stopped.

HOWARD H. RAMBO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 773,523 Richards Oct. 25, 1904 1,560,041 Christensen Nov. 3, 1925 1,863,851 Hughes June 21, 1932 2,074,738 Aikman Mar. 23, 1937 2,187,712 Neeson Jan. 16, 1940 2,212,631 Baker Aug. 27, 1940 2,317,135 Crittenden Apr. 20, 1943 2,380,226 Frantz July 10, 1945 2,410,824 Lamberton Nov. l2, 1946 2,421,872 Evelyn June 10, 1947 FOREIGN PATENTS Number Country Date 529,417 Germany 1931 

